[Skimmertalk] I'm trying to build a common mode choke for 2, 200 and 630 meters and don't know what I'm doing

[Tom Berry]

Wes,  I would be interested in what you end up using and if it's worth 
the effort.

73 Tom AA4VV

On 11/18/2017 6:42 PM, Wes Cosand wrote:
> Let's try this a third time
>
>   I need some help.
>
>
>
> Jack Smith, K8ZOA (SK), wrote an impressive web page some years ago
> describing how he improved the performance of his active vertical antenna
> using chokes at both ends of the coax.
>
> https://web.archive.org/web/20150803213958/http://www.clifto
> nlaboratories.com/vlf_signals_with_improved_setup.htm
> <https://web.archive.org/web/20150803213958/http:/www.cliftonlaboratories.com/vlf_signals_with_improved_setup.htm>
>
>
>
>   I am trying to replicate that although using a different active antenna.
> But it isn't trivial to find toroids that provide much impedance at
> 100kHz.  It is my understanding that the most appropriate easily available
> Fair-Rite mix is their type "75".
>
>
>
> I bought 25 Fair-Rite 5975001801 toroids from Mouser.  They have an
> internal diameter of only 0.54 inches so I bought some RG-174-U planning to
> use about a dozen toroids at each end of the cable.  But I was surprised
> how few turns I could get through a stack of toroids, especially if I wound
> them in reasonably tightly.  Here is a photo of my attempt:
>
> https://photos.app.goo.gl/zeRaPbKiDViWIvJj2
>
>
> This toroid has an A of 3,025 nH.   Using the formulas in
> http://ka7oei.blogspot.com/2017/11/a-semi-typical-suburban-e-field-whip.html
> I calculate something like an impedance of 6900 ohms for these 25 toroids
> at 100 khz.
>
> Mouser stocks a type 75 toroid with an internal diameter of 1.4 inches with
> an A of 6850.
>
> How do I do this better?  Even putting a crimp BNC on coax is a new
> experience for me and I am feeling incompetent.  When I put this assembly
> on the receiver end of the coax before the coax power supply I observe very
> little obvious difference in the noise level at 136 kHz in HDSDR.  Is that
> expecting too much?
>
> Am I "straining at gnats and swallowing camels"?
>
>
>
> Wes WZ7I
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